(1) Field of the Invention
The present invention relates to image forming devices such as printers, and to charging methods for secondary batteries.
(2) Description of the Related Art
An image forming device, such as a printer, is provided with an image forming unit that executes an image forming job of forming an image on a recording sheet, and a reception unit such as an interface that receives an execution request for the image forming job. With respect to such an image forming device, a proposal is being made of a configuration for realizing a system using both power from a secondary battery such as a nickel-hydrogen battery and power from an external power source such as a commercial power supply. An image forming device with such a configuration switches between a sleep mode and an operation mode.
The sleep mode is a mode of the image forming device in which, when the image forming unit is not executing an image forming job, the reception unit is not supplied power from the external power source, is supplied power from the secondary battery, and is able to receive an execution request for an image forming job. The operation mode is a mode of the image forming device in which, when an execution request for an image forming job is received, the image forming unit executes the image forming job by using power from the external power source.
By making such a configuration where an image forming job is executed when the image forming device is in the operation mode and the image forming device switches to the sleep mode when an image forming job is not being executed, energy can be conserved since power from the commercial power supply is not used when the image forming device is in the sleep mode. Furthermore, by making such a configuration, power from the secondary battery is supplied to the reception unit when the image forming device is in the sleep mode, and thus, an execution request for an image forming job can be received when the image forming device is in the sleep mode.
When adopting the above-described configuration of switching between different modes, it suffices that charging of the secondary battery is performed when the image forming device is in the operation mode, and discharging of the charged secondary battery is performed when the image forming device is in the sleep mode.
In addition, such an image forming device is typically provided with a power supply unit that converts a voltage from the external power source into a voltage suitable for the operation of the image forming unit and outputs the voltage. Further, for charging the secondary battery, a circuit configuration is often adopted including a booster circuit that boosts the voltage outputted by the power supply unit to the voltage necessary to fully charge the secondary battery, and supplies the boosted voltage to the secondary battery. By adopting such a circuit configuration, the secondary battery can be fully charged while utilizing a conventional power supply unit.
When the circuit configuration described above, which uses the booster circuit, is adopted, a considerable power loss occurs when the voltage is changed, or in other words boosted, to the boosted voltage. Therefore, the state of power loss continues from when charging of the secondary battery is started until when the secondary battery is fully charged. As such, the efficiency of charging of the secondary battery is decreased.
Such a technical problem is not only limited to occurring when adopting the configuration of switching between the sleep mode and the operation mode, but can occur in any configuration where a reception unit, such as an interface, is driven by being supplied with power from a secondary battery